Preprint study evaluated entire Scottish population and calls into question delaying second Covid vaccine dose up to 12 weeks. After first dose it noted a drop in preventing hospitalization from 84% at 5 weeks to 58% after the 7th. And after 16 weeks?

Medical Mythbusting Commentary for April 30, 2021

Scotland’s vaccine rollout suggests delaying the 2nd COVID-19 shot is a bad idea

Effectiveness of first dose of COVID-19 vaccines against hospital admissions in Scotland:
national prospective cohort study of 5.4 million people